1. Field of the Invention
Flavobacterium columnare is an aquatic bacterium that is highly infectious in both warm and cold water species of fish. In the channel catfish (Ictalurus punctatus), it is the causative agent of columnaris disease. Flavobacterium columnare is a Gram-negative, rod shaped, pathogen that has been isolated from channel catfish in areas of the southeastern United States where this species is cultured. The disease also affects sports fish (i.e., walleye and largemouth bass) and aquarium fishes. Medicated feed (antibiotics) is currently used to try and control this bacterial infection. However, these treatments are limited in their effectiveness and most producers have discontinued use of medicated feeds. Prevention of columnaris disease by vaccination is an important goal and a top priority of catfish and other fish producers throughout the world. Estimated savings to these industries would be in excess of $100 million annually.
This invention relates to a novel vaccine against columnaris which does in fact provide superior protection over commercial treatment involving treating the water with potassium permanganate (KmnO4) or feeding medicated feeds.
2. Description of the Prior Art
It has been estimated that columnaris is the second leading cause of mortality in pond raised catfish in the southeastern United States. Based on the success of disease control by immunization with killed bacteria (i.e., bacterins) in salmonids, experimental bacterins have been developed and tested against F. columnare. However, no vaccine is currently available and vaccination is not practiced in the catfish industry against F. columnare, presumably because the inactivation (i.e., formalin treatment) destroys the antigen (Bader et al., Comparison of whole-cell antigens of pressure-and formalin-killed Flexibacter columnaris from channel catfish (Ictalurus punctatus), American Journal of Veterinary Research, 58, pp 985-988, 1997). The patent of Wolf-Watz et al. (U.S. Pat. No. 5,284,653) presents a whole list of bacteria of which one is Flexibacter columnaris (now F. columnare) which has the potential to be genetically modified to produce a vaccine. However, no data are presented on F. columnare vaccines, only on genetically modified mutant vaccines of Vibrio anguillarum. Bernadet (Immunization with bacterial antigens: Flavobacterium and Flexibacter infections, Fish Vaccinology: Developments in Biological Standardization, Volume 90, pp 335-340, 1997; Karger Switzerland: Basel) reviews the limited knowledge available on F. columnare and vaccination against this important disease. Work suggests that rainbow trout (Oncorhynchus mykiss) which survive infection with F. columnare are immune to subsequent disease.